Temperature-sensitive polypeptide nanogels for intracellular delivery of a biomacromolecular drug

Temperature sensitive nanogels prepared from ionic complexes of positively charged poly(ethylene glycol)-poly(l-lysine)-poly(l-alanine) (PEG-PK-PA) and negatively charged hyaluronic acid (HA) were investigated as intracellular delivery vehicles of a biomacromolecular drug of fluorescein isothiocyanate conjugated bovine serum albumin (FITC-BSA). By varying the weight ratio of the polymer to hyaluronic acid from 100/0 to 19/81, the zeta potential of the nanogel could be controlled from +47 mV (100/0), 0 mV (67/33), and -47 mV (35/65). In particular, the nanogels prepared from 67/33 exhibited 0 mV, and the size was reversibly changed from 220 nm at 20 °C to 160 nm at 37 °C with a narrow size distribution. The internalization of the FITC-BSA loaded nanogel was significantly affected by the zeta potential. In particular, the nanogel with zero zeta potential was very effective in internalizing the model drug. The cells treated with chlorpromazine significantly reduced the internalization efficiency, suggesting that clathrin mediated endocytosis is the main mechanism of the internalization of the nanogel. Cytotoxicity measured by the MTT assay suggested that the PEG-PK-PA/HA ionic complex nanogel is significantly less cytotoxic than PEG-PK-PA itself. This paper suggests that (1) the PEG-PK-PA/HA nanogel could be tightened by heat-induced shrinkage, (2) the internalization efficiency of the nanocarrier could be controlled by modulating the size and zeta potential of the nanogel, and (3) cytotoxicity of the positively charged nanogel was significantly improved by the formation of the ionic complex with negatively charged hyaluronic acid.